1. Technical Field
The present invention is directed toward communication devices, and more particularly toward full-duplex radio frequency communication devices.
2. Background Art
Radio frequency (RF) communication systems, such as cellular telephone systems, are designed to handle maximum capacity with limited channel frequencies. A time division multiple access (TDMA) system subdivides time on each frequency into time slots that can be assigned to different users. A code division multiple access (CDMA) system, including wideband CDMA (WCDMA), spreads a digitized signal using a code and utilizes the assigned frequency at all times.
During operation, a cellular communication device may be required to engage in an inter-frequency handover or handoff. To perform a handoff, the cellular communication device receiver must perform certain activities such as making power measurements, acquiring control channels and/or engage in handoffs. These activities require the cellular communication device to receive signals on two separate frequencies.
The standard structure for allowing such operation is to have two receivers, from RF to baseband, so that each receiver will be able to make its required measurements while on a call and/or receiving data. However, use of two complete receivers is not economical for such communication devices, particularly given the cost competition that is well-known in various telecommunications markets.
Another solution is to use a slotted mode for the receiver, wherein a time slot is created for measurements without breaking the continuous receive link. The created slot enables the receiver to jump to a different frequency to make power measurements and/or acquire control channels. This solution allows for the sharing of the entire receive chain, but also requires that the device have two full channel stepping synthesizers, since transmission may still occur while a new receive frequency is being detected.
Normal full-duplex CW radios have a fixed spacing between the transmit frequency and the receive frequency (e.g., 190 MHz in the case of the known non-US 3rd generation spectrum). Typically, a single channel stepper is used with an offset loop to provide the fixed spacing. The channel stepper generates the frequency for the receiver and the offset loop generates the transmit frequency using the fixed spacing. However, when a new receive frequency has to be used, the fixed relationship between the transmit and receive frequencies is broken so that one 2 GHz stepping synthesizer is not sufficient. Typically, 2 GHz is appropriate for the 3rd generation non-US spectrum with frequencies in the transmit band from 1920 MHz to 1980 MHz on a 200 KHz grid and for frequencies in the receive band from 2110 MHz to 2170 MHz that may also be on a 200 KHz grid. While slotted mode operation can eliminate the need for two costly receivers, in the 3rd generation non-US spectrum example given, two 2 GHz channel steppers (one for receive and one for transmit) may still be required since there is no continuously fixed spacing between the receive and transmit frequencies. The known difficulty with making such high frequency channel steppers can translate to high costs and high current consumption.
Consequently, a need exists for minimizing radio hardware necessary for performing activities and/or measurements associated with an inter-frequency handover that may be required in a telecommunication system operating in a non-TDMA standard, such as, for example, the WCDMA standard.
The present invention is directed toward overcoming one or more of the problems set forth above.
It is an object of the invention to provide a low cost RF full-duplex communication device which uses minimal current.
It is a further object of the present invention to attend to the inter-frequency receive activities required in WCDMA systems with a minimum of radio hardware.
It is a feature of the invention to utilize a sole transmitter and a sole receiver.
It is a further feature of the present invention to assign a high frequency channel stepper directly to the generation of a transmit signal.
In one aspect of the present invention, a communication device is provided for full-duplex radio communication in a selected range of channels where the channels are spaced by a selected increment. A transmitter and a receiver are connected to a duplexer for simultaneously transmitting and receiving signals. A high frequency channel stepper is connected to the transmitter to selectively shift frequency in steps substantially equal to the selected increment. A low frequency offset channel stepper is selectively connected between the high frequency channel stepper and the receiver and is adapted to selectively shift frequency either a first selected offset amount or one or more out of a selected set of offset amounts.
In one embodiment of the invention, the first-selected offset amount is a designated duplex spacing between the transmit frequency and the receive frequency.
In another embodiment of the invention, the selected set of offset amounts are different from the first selected offset amount.
In still another embodiment, a controller is provided and adapted to (a) selectively connect the high frequency channel stepper directly to the receiver when the device is in a camping mode not transmitting a signal, (b) selectively connect the high frequency channel stepper through the low frequency offset channel stepper and cause the low frequency offset channel stepper to shift frequency the first selected offset amount when the device is in a normal communicating mode, and (c) selectively connect the high frequency channel stepper through the low frequency offset channel stepper and cause the low frequency offset channel stepper to shift frequency at least one of the selected set of offset amounts when the device is in a slotted communicating mode.
In yet another embodiment, a switch is provided having a first position connecting the high frequency channel stepper to the receiver through the low frequency offset channel stepper and a second position connecting the high frequency channel stepper directly to the receiver.
An advantage of the present invention is that manufacturing costs are decreased.
Another advantage of the present invention is that current consumption is reduced during camping mode.